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Monkeysailor's Photo Lab 



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Monkeysailor's Photo Lab 

Written By: Andrew Lewis 



f TOOLS: 



Adjustable clamps (2) 

Band saw (1) 

for cutting PVC and sheet aluminum 

Computer (1) 

Drill (1) 

Glue gun (1) 

Pop rivet tool (1) 

Scissors (1) 

Screwdrivers (1) 

Soldering equipment (1) 

Wire strippers (1) 



© PARTS: 



Paterson film developing tank (1) 

Film developing chemicals (1) 

Film changing bag (1) 

Arduino-compatible microcontroller 

board (1) 

I used a Seeeduino. 

PC power supply unit (PSU) (1) 

Servomotor (1) 

/ used a Futaba S3001 . 

LCD display (1) 

/ used a Hitachi HD44780. 

Circuit board (1) 

for display buttons. I etched my own 
PCB (download the mask at 
makeprojects.com/v/31). You can also 
use plain perf board, about 4" square. 

Temperature sensors (2) 

Switches (8) 

Transistors (2) 

to control the heater elements. You 



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Monkeysailor's Photo Lab 



could also use a smaller transistor like a 
2N222 to trigger a relay, and a diode to 
mop up any back EMF from the relay 
coil. 

resistors (9) 

resistors (3) 

resistors (1) 

Potentiometer (1) 

Speaker (1) 

Adapter cable (1) 

Spade (4) 

Pin headers (1) 

These make it easier to connect wires to 

the Arduino securely. 

Wired) 

for signal connections 

Wired) 

for power connections; I used multicore 

Power Flex from an old appliance. 

nichrome wire (1) 

/ used old heater wire that has a 

resistance of about 2C1 per yard. 

Wired) 

Wired) 

Wooden case (1) 

/ got one from Mines Design Labs 

(angushines. com). 

Plastic sheet (1) 

It won't be visible, so it's OK if it's 

damaged. 

Aluminum sheet (1) 

Tin can (1) 

for the Paterson tank warmer. I used a 



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Monkeysailor's Photo Lab 



cigar can; a big soup can will also work. 

Panel printout (1) 

on thick paper or printable plastic film. 

You can design your own or download 

mine. 

Furnace cement (1) 

aka fire cement or refractory cement, to 

encase the heater coils 

Various fasteners (1) 
for mounting the warmers 

MeshM) 

to cover the vent 

Fiberglass insulation (1) 

Silicone sealant (1) 



SUMMARY 

Traditional photography is fantastic. I love the way mechanical cameras feel in my hand, and 
I love the way film makes me think about composition and lighting before I actually take a 
shot. The only thing I don't like about traditional photography is the cost of having film 
processed or buying equipment to develop my own. 

To cut costs and have a little fun with an Arduino along the way, I decided to make my own 
film processor. The equipment needed to turn a roll of exposed medium-format color film into 
negatives actually isn't that complicated, and the chemical process is also straightforward. 
Using a standard developing tank and chemicals, all you really need are a stable working 
temperature and accurate timing, which you can accomplish using an Arduino, an LM35 
temperature sensor, and a few electrical components. 

To develop film, you immerse it in developer at a specific temperature for a specific amount 
of time, agitate it every few seconds to ensure an even process across the film, then repeat 
the process with fixer/blix solution, and repeat again with rinse water. This can be done in a 
Paterson tank, which lets you pour liquids in and out without exposing the film inside to any 
light. With a film-changing bag to load the film into the tank, you don't need a darkroom! 



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Monkeysailor's Photo Lab 

Different film types or chemicals require different times and temperatures, and the 
brightness, contrast, or color will not develop correctly if they're wrong. So I needed to work 
out a system that would maintain and monitor the temperature of 4 chemical bottles, and 
time the processing down to the second. 

I also thought it would be handy if my Photo Lab could agitate the film automatically, and 
store my time and temperature settings so I wouldn't have to reprogram them with each 
batch. For the auto-agitation, I used a hobby servomotor, and for programming I designed a 
control panel around a Hitachi HD44780 16x2 LCD display, with pushbuttons for making 
menu selections. The buttons let you move through the menu screens, increase and 
decrease heater, timer, and agitation values, and save/restore the settings to the Arduino. 

With the agitator, timer, and menu system, the Photo Lab project plans grew larger than my 
original idea for a chemical warmer, but I was confident I could make it all work. At one point 
I realized that although I had set my sights on a photographic processor, my system would 
be great for warming any liquids. With a little modification, it could be used to control 
hotplates, furnaces, and fish tank heaters for other projects. 



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Monkeysailor's Photo Lab 




• Download the code, schematics, and templates . 

• At first, the Arduino I/O pins seemed out-numbered by the connections needed for the LCD 
screen, temperature sensors, servo, and pushbuttons. 

• To get around this problem, I made a custom PCB with all the buttons wired in parallel to a 
resistor array with different-value resistances along each path. Each button press 
produces a different voltage through the board, which lets the Arduino read all the buttons 
from a single analog input pin. 

• For power, I used a standard ATX power supply unit (PSU) for tower PCs. These provide 
plenty of amps, have a built-in fan and surge protection circuit, and make available a nice 
selection of voltages via their 20- or 24-wire cable that connects to the PC motherboard. 

• To turn the power supply on, you connect its green and black (ground) wires, and then the 
yellow and red wires supply +12V and +5V, respectively. 

• I wired my circuitry to the PSU via a cut ATX adapter cable, which saved me from cutting 
the PSU's own cable, but you could cut and solder the unit's wires directly. I connected the 
Arduino to a 12V line. I could have bypassed the Arduino's internal voltage regulator and 
connected it directly to 5V, but felt that it wasn't necessary. 



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Monkeysailor's Photo Lab 




To button PCB 
To button PCB 



Temp sensor few 
Patterson tank heater 

T&mp sensor for 
bottle heater 




To speaker via lh resistor 
Pin 4 of LCD 
Pin 6 of LCD 

Control wire to servo 

Transistor for Patterson tank heater 

Transistor for bottle heater 

Pin 11 of LCD 

Pin 12 Of LCD 

Pin 13 of LCD 

Pin 14 of LCD 

U&ltage for thermistors 




• See the photo for a diagram of the Photo Lab's microcontroller connections. I glued the 
button PCB and LCD screen onto a sheet of PVC with holes for the display and buttons. I 
made a larger aluminum sheet (195mmx 175mm) with matching cuts to the front, drilled its 
corners for screw mounting to the main box, and glued the aluminum onto the PVC. 

• I chose an LCD display without backlighting to use the Photo Lab in a darkroom, and 
powered it with 12V from the power supply. Following the LCD's datasheet, I connected a 
small potentiometer to control the contrast, and glued it to the back of the pane. 

• After I connected the LCD and speaker to the Arduino and glued them to the PVC, the 
interface hardware was complete. 

• A designer friend came up with a nifty retro design for a panel cover, styled after an old 
camera, which I printed onto a sheet of plastic film. Aside from making the panel look 
pretty, this cover acts as a splash guard for the push buttons. 

• Finally, I made sure everything was glued securely in place, and I uploaded my Arduino 
sketch to the microcontroller for testing. 



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Monkeysailor's Photo Lab 




• Now that I had my panel, I could use it to control and sense things in the real world. 

• I experimented with thermistors and thermocouples, but decided to use two LM35 solid- 
state temperature sensors, one for the chemical bottles and one for the developing tank. 
These sensors are accurate to about 0.5°C, which is good for sensitive color film 
processing. 

• I powered them in parallel from the Arduino's D1 pin, and for greater accuracy, they're only 
powered up when they're about to take a reading. Continuously supplying them with power 
generates a bit of heat that can throw their readings off. 



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Monkeysailor's Photo Lab 





• I attached the servomotor to the lid 
of my developing tank with hot 
glue, and added a stirrer to the 
servo shaft using bent wire. To 
avoid the tank lid being 
permanently attached to the Photo 
Lab along with the servo, I added a 
servo connector to the top, which 
is wired to the main board's power, 
ground, and Arduino pin D8 for 
control. 



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Monkeysailor's Photo Lab 







To make a bottle holder, I measured the 4 bottles that I use to store developing chemicals, 
and constructed an aluminum box to fit neatly around them. I used thin aluminum sheets, 
and riveted them to aluminum angles at the corners. The pairs of side pieces measured 
90mmx 150mm and 320mmx 180mm, and the bottom piece measured 90mmx320mm. 

For the heating, I wound Nichrome heating wire around a screwdriver to make 4 coils. I 
connected these in parallel between 2 copper power wires, and sat one under each bottle 
in the bottom of the aluminum box. 

The coils are powered by the 5V line from the PC power supply, switched by a STP36NF06 
transistor controlled by Arduino pin D6. Alternative coil winding and voltages will produce 
different results, so you can tailor the element design to suit your needs. 

I wound the heater wire into coils and set into fire cement at the bottom of the box with the 
power wires sticking out one end. I added another sheet of aluminum to close the bottom 
of the box, and sealed with silicone. 

I mounted the temperature sensor on the bottom of the aluminum box near the wires that 
lead to the heating element. The sensor connects to Arduino analog pin A5. I did think 
about suspending it inside one of the bottles, but I felt that having the sensor on the 
element would be neater. 



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Monkeysailor's Photo Lab 




• Paterson developing tanks are cylindrical, so instead of making a holder out of sheet 
metal, I used an old cigar can that fit it nicely. A large soup can also works. 

• I drilled a hole in each side of the tin and fitted a Nichrome coil in place with fire cement as 
I'd done with the bottle warmer. 

• Finally, I glued the temperature sensor to the tin with epoxy resin. This heater coil is 
controlled by a transistor connected to Arduino pin D7 and the sensor feeds into pin A4. 








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The laser-cut Photo Lab case was manufactured from birch-faced plywood by my friends 
over at Hines Design Labs. I designed the case to accept an ATX power supply, and 
before I fitted it in, I covered the air intake with wire mesh. 

You can see my templates in the zip file from Step 1 . You can also add panel artwork like 
the 3rd image from John Ranford. 



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Monkeysailor's Photo Lab 





• I connected several of the power 
supply's 5V (red) lines together so 
they could handle the current for 
the heater elements. The power 
switch for the PSU acts as the 
power switch for the Photo Lab, 
and I connected the green and 
black ATX wires together so that 
the PSU supplies power as soon as 
it's plugged in and turned on. 

• I fit the aluminum box and cigar 
can into the project box using a 
combination of wooden blocks, 
Meccano brackets, wood screws, 
and wood glue. 

• Nothing inside the box should get 
hotter than 140°F (60 °C), so I 
didn't make any special effort to 
protect the wood. As a final 
measure, I packed some fiberglass 
thermal insulation around the 
heaters. 



The Big Picture 

I'm very pleased with this project, and I now use it to process my rolls of film. The only problem 
so far is that the heaters take a long time to bring the bottles up to temperature, so I think I might 
replace the elements with 12V or 240V versions. This should be easy because it involves no 
modifications beyond exchanging the transistors for solid-state relays. 

The timer and auto agitator take all the stress out of processing film, and mean that I don't have 
to keep an eye on the clock. I can leave the film to process and trust that the tank will be stirred 
every few seconds. 



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Monkeysailor's Photo Lab 



The processor is also handy for developing black and white film using weak solutions to achieve 
finer grain, which is a slow process. Experimental developers such as caffeine (yes, caffeine!) 
can take more than half an hour to process, and my Photo Lab machine lets me avoid a nasty 
hand cramp from manually stirring a tank for 30 minutes. 

This project first appeared in MAKE Volume 31 , page 123. 

This document was last generated on 201 2-1 1 -03 01 :52:26 AM. 



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